The subject matter disclosed herein relates to an environmental control system and, more particularly, a multi-zone temperature control system.
A typical heating, ventilation and air conditioning (HVAC) system with multi-zone temperature control targets includes a multi-stage or variable speed heat pump (HP), a blower and multiple dampers. In a heating mode, a furnace may be used to replace the HP to provide heat or an electrical heater may be used to supplement the HP to provide heat in cold weather.
Often, HVAC systems further include zone controllers and a system demand controller. Individual zone controllers are respectively associated with temperature control in each zone and may employ a damper to control the zone temperature based on information about the temperature set-point and each zone temperature measurement. By contrast, the system demand controller is used to control the HP (or the furnace or the electrical heater) based on a total demand of each zone (i.e., the difference between zone temperature and its setpoint for each zone).
A typical HVAC system is described in U.S. Pat. No. 7,377,450, the entire contents of which are incorporated herein by reference, and is shown schematically in FIG. 1. Such a system includes a heat pump 10 to supply refrigerant to a coil 11 and a blower 12. The blower 12 blows air over the coil 11 to cool the air in a cooling mode or to heat the air in a heating mode, and the air is then directed to ductwork 13 that is fluidly coupled to zones 1-6 (here 6 zones are only used for illustration purpose and could be single or multiple zones in fewer or greater numbers). The cooled or heated air is supplied to the zones 1-6 via dampers 1-6, which are respectively associated with each of the zones 1-6. Sensors within each zone measure temperatures therein with those measured temperatures subsequently employed in the calculation of zone errors based on predefined setpoints. The zone errors and noise limits for each zone are provided to system demand controller 14, which is coupled to the heat pump 10 and which may be a heat pump proportional integral (PI) controller, and the zone controllers 15, which are coupled to each of the dampers 1-6 and which may be PI controllers for each of the dampers 1-6.
The zone errors define the demand for heat pump 10 capacity and the noise limits define an amount of air to be permitted to flow into each of the zones 1-6 via the dampers 1-6. Thus, if there is an increased demand for heat pump 10 capacity, the system demand controller 14 will instruct the heat pump 10, the coil 11 or the blower 12 to output more cooled air in cooling mode or heated air in heating mode to the ductwork 13. By contrast, the zone controllers 15 will open or close each of the dampers 1-6 based on whether the air flow into the zones 1-6 exceeds the noise limits for each respective zone.
With the configuration described above, it is possible that the system demand controller 14 could be driven to provide too much heating/cooling capacity to the zones 1-6 even though such capacity cannot be delivered to the zones 1-6 by the corresponding zone controllers 15 due to air flow constraints imposed by the noise limits on each zone. For such cases, the current HVAC systems employ system demand controllers 15 that are forced to use exceptional rules to satisfy the air flow constraints.